The present invention relates to the building materials intended for the manufacture of building structures and articles and, more specifically, to a concrete mix and processes for the manufacture of chemically stable structures operating under the conditions of strongly aggressive liquid or gaseous media having predominantly an acidic reaction.
The concrete mix according to the present invention is useful in the manufacture of both supporting and self-supporting, mainly reinforced structures, as well as non-reinforced articles having different dimensions and shape,
Different concrete mixes employed for the manufacture of chemically stable structures and articles to be used under the conditions of aggressive media are known among the most widespread concrete mixes recently employed are the polymer-concrete mixes, wherein as a binding agent use is made of various synthetic resins: epoxy, unsaturated polyester resins, phenolic, furan, carbamide, polyurethane, acrylic resins and the like.
These materials generally possess high durability characteristics and an increased chemical stability. However, they are too expensive and have high toxicity in the manufacture. Another essential disadvantage of all the above-mentioned materials based on synthetic resins resides in their inflammability and a low heat-resistance, as well as a limited stability in oxidizing acids.
Also known are acid-resistant concretes incorporating water glass, acid-resistant fillers and aggregates and modifying admixtures. As a curing agent in such concrete mixes use is generally made of salts of fluosilicic acid. Such concrete mixes are widely employed for the manufacture of prefabricated and monolithic structures operating under the conditions of acidic aggressive media. A disadvantage of these concrete mixes is their insufficient mechanical strength not exceeding 250 kgf/cm.sup.2 (compression) and a low water-resistance. Furthermore, salts of fluosilicic acid are very toxic and cause corrosion of steel reinforcement members. The process for the manufacture of structures from such mixes comprises intermixing water glass with aggregates, moulding of the ready mix in a mould, followed by heat-treatment thereof at a temperature of from 80.degree. to 120.degree. C.
Recently in the Soviet Union there has been developed a material known as silicoconcrete containing a high silica-content silicate clod, finely ground quartz sand, general sand, rubble and water. The silicoconcrete features high mechanical strength properties; thus, its compression strength is 500 kgf/cm.sup.2 ; it also has a high density. Acid-stability of silicoconcrete is at least 97%. Such concrete mixtures are employed for the manufacture of prefabricated reinforced concrete members.
The process of manufacturing such prefabricated members involves moulding and densification of the final mix and a heat-moisture treatment by the schedule: pressure elevation in an autoclave up to 12 atm for 3-4 hours, curing under 12 atm-21 hours, releasing pressure to zero over 3-4 hours. However, silicoconcrete has some disadvantages caused by certain difficulties in the preparation of a special high-silica-content glass, associated with the necessity of using very high temperatures (up to 1,580.degree. C.) for its smelting. Moreover, for hardening the products made from ceramsite concrete, curing is necessary under a high pressure for a long period. All this results in a complicated process technology and, hence, in an increased cost of production of the final articles.
Concrete mixes for the manufacture of acid-resistant articles incorporating water glass, finely ground perlite, perlite sand and andesite rubble are also known in the art.
Such mixes have but insufficient mechanical strength and a low water-resistance. The process for the manufacture of articles from such mixes comprises mixing of aggregates with liquid glass, followed by moulding and heat-treatment of the moulded articles. Prior to the heat-treatment the moulded articles are subjected to a 4-day curing and the heat-treatment is conducted as follows: heating within the range of from 50.degree. to 70.degree. C. for 3 hours, within the range of from 80.degree. to 100.degree. C. for 2 hours; at a temperature of from 120.degree. to 150.degree. C. for 3 hours. The resulting acid-resistant articles have an ultimate compression strength of 280-290 kgf/cm.sup.2, bending strength--96-100 kgf/cm.sup.2. This process for the manufacture of acid-resistant articles does not enable the production of high-strength, dense steel-reinforced articles.